// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/rand_util.h"

#include <errno.h>
#include <fcntl.h>
#include <stddef.h>
#include <stdint.h>
#include <unistd.h>

#include "base/files/file_util.h"
#include "base/lazy_instance.h"
#include "base/logging.h"

namespace {

// We keep the file descriptor for /dev/urandom around so we don't need to
// reopen it (which is expensive), and since we may not even be able to reopen
// it if we are later put in a sandbox. This class wraps the file descriptor so
// we can use LazyInstance to handle opening it on the first access.
class URandomFd {
public:
    URandomFd()
        : fd_(open("/dev/urandom", O_RDONLY))
    {
        DCHECK_GE(fd_, 0)/* << "Cannot open /dev/urandom: " << errno*/;
    }

    ~URandomFd() { close(fd_); }

    int fd() const { return fd_; }

private:
    const int fd_;
};

base::LazyInstance<URandomFd>::Leaky g_urandom_fd = LAZY_INSTANCE_INITIALIZER;

} // namespace

namespace base {

// NOTE: This function must be cryptographically secure. http://crbug.com/140076
uint64_t RandUint64()
{
    uint64_t number;
    RandBytes(&number, sizeof(number));
    return number;
}

void RandBytes(void* output, size_t output_length)
{
    const int urandom_fd = g_urandom_fd.Pointer()->fd();
    const bool success = ReadFromFD(urandom_fd, static_cast<char*>(output), output_length);
    CHECK(success);
}

int GetUrandomFD(void)
{
    return g_urandom_fd.Pointer()->fd();
}

} // namespace base
